The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board (PCB) attached to a disk drive base of the HDA. The head disk assembly includes at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The spindle motor typically includes a rotating hub on which disks are mounted and clamped, a magnet attached to the hub, and a stator. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet, thereby rotating the hub. Rotation of the spindle motor hub results in rotation of the mounted disks. The printed circuit board assembly includes electronics and firmware for controlling the rotation of the spindle motor, for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host.
The head stack assembly typically includes an actuator, at least one head gimbal assembly (HGA), and a flex cable assembly. Each HGA includes a head for reading and writing data from and to the disk. In magnetic recording applications, the head typically includes an air bearing slider and a magnetic transducer that comprises a writer and a read element. The magnetic transducer's writer may be of a longitudinal or perpendicular design, and the read element of the magnetic transducer may be inductive or magnetoresistive. In optical and magneto-optical recording applications, the head may include a mirror and an objective lens for focusing laser light on an adjacent disk surface.
During operation of the disk drive, the actuator must rotate to position the heads adjacent desired information tracks on the disk. The actuator includes a pivot bearing cartridge to facilitate such rotational positioning. One or more actuator arms extend from the actuator body. An actuator coil is supported by the actuator body opposite the actuator arms. The actuator coil is configured to interact with one or more fixed magnets in the HDA, typically a pair, to form a voice coil motor. The printed circuit board assembly provides and controls an electrical current that passes through the actuator coil and results in a torque being applied to the actuator. A crash stop is typically provided to limit rotation of the actuator in a given direction, and a latch is typically provided to prevent rotation of the actuator when the disk drive is not in use.
Many modern HDAs include a ramp adjacent the disk outer periphery. In such HDAs, each HGA (itself attached to the distal end of an actuator arm in the HSA) typically includes a lift-tab. The lift-tab is designed to contact a lift-tab supporting surface of the ramp when the actuator moves near an extreme position that is typically beyond the disk outer periphery. To prevent the heads from sliding off of the outer edge of the disk before they are properly unloaded, a portion of the ramp (that includes a portion of the lift-tab supporting surface) typically must extend over the disk outer periphery. That portion of the ramp overlaps the disk.
Typically at the beginning of a period when the disk drive is not in use, the actuator rotates the HSA so that each HGA's lift-tab contacts a corresponding lift-tab supporting surface, in a lift-tab pick-up region of that lift-tab supporting surface, to unload the heads from the surface of the disk. Then the actuator continues to rotate so that each of the lift-tabs slides over the lift-tab supporting surface to a lift-tab parking region where it will remain while the disk drive is not in use.
The benefits of unloading the heads can include improved tribological performance and reliability of the head-disk interface and improved robustness to mechanical shocks that are suffered under non-operating conditions. For example, unloading and parking the heads can improve robustness to mechanical shocks during periods of disk drive non-operation because, when unloaded and parked, the heads are not physically adjacent disk surfaces. Therefore, the heads are less likely to impact and thereby damage the disk surface in response to mechanical shocks.
However, during periods of operation of the disk drive the ramp does not separate the heads from adjacent disk surfaces, so that the relative motion excited by mechanical shocks may cause the heads to slap adjacent disk surfaces, thereby damaging those surfaces. The relative motion excited by mechanical shocks during disk drive operation also may cause impacts between other HGA components (such as the swage plate) or HSA components (such as an actuator arm), and one or more adjacent disk surfaces. The relative motion excited by mechanical shocks may also cause impacts between the outer periphery of one or more disks and corresponding overlapping portion(s) of the ramp. Energy transferred from one disk drive component to another via such impacts can exacerbate the relative motion that leads to other, potentially more damaging impacts.
Impacts between the outer periphery of one or more disks and the overlapping portion(s) of the ramp may be avoided for some mechanical shocks via the nominal clearance between the two components. That is, if a mechanical shock is minor enough so that the total relative travel of the disk outer periphery relative to a corresponding overlapping portion of the ramp is less than the clearance between the two, then the disk outer periphery will not impact the corresponding overlapping portion of the ramp, and so further excitation of disk vibration from such an impact would be thereby avoided.
However, typical specifications for mechanical shock robustness in the disk drive industry continue to become more stringent, especially for disk drives designed for mobile applications. To meet such specifications the disk drive must be able to survive more severe mechanical shocks during operation and during non-operation. More severe shocks may cause impacts between the disk outer periphery and the ramp despite the existence of a nominal clearance between the two, and the nominal clearance may not be practically increased to the extent necessary to prevent such impacts because of dimensional constraints.
Thus, there is a need in the art for an improved ramp configuration that can reduce the consequence of impacts between the outer periphery of one or more disks and corresponding overlapping portion(s) of a ramp, due to mechanical shocks that may occur under operating conditions or non-operating conditions.